Self-coated single crystal, and production apparatus and process therefor

Abstract

It is an object of the present invention to provide a self-coated single crystal that without any special step conducted after crystal growth, has its circumference coated with a layer of different properties. A self-coated single crystal according to the present invention is characterized in that in operations comprising melting crystal materials for a core and a clad in a single crucible and carrying out growth of a single crystal through a pulling up method or a pulling down method, a grown single crystal in an as-growth condition has its circumference self-coated with a clad whose refractive index is lower than that of the core.

1 . A production method of a self-coated single crystal characterized by comprising: melting materials having different melting points in a single crucible; providing such a temperature gradient as a temperature is lowered from a central portion toward an edge portion on a solid-liquid interface; and carrying out crystal growth by a pulling down or pulling up method. 
   
   
       2 . The production method of a self-coated single crystal according to  claim 1 , wherein a planar protruding portion having an outer diameter which is not greater than fivefold of an inner diameter (B) of the crucible is provided around a hole formed in a bottom portion of the crucible on an exit side to grow the single crystal. 
   
   
       3 . The production method of a self-coated single crystal according to  claim 2 , wherein 1.2<(B/)<5 is achieved. 
   
   
       4 . The production method of a self-coated single crystal according to  claim 3 , wherein 1.5<(B/S)<4.5 is achieved. 
   
   
       5 . The production method of a self-coated single crystal according to  claim 1 , wherein an outer side of the melt is cooled by flowing an inert gas from a lower side toward an upper side of the crucible, thereby realizing a desired temperature gradient. 
   
   
       6 . The production method of a self-coated single crystal according to  claim 1 , wherein a material serving as the clad material is a material obtained by adding a rare-earth element or a transition element in a material serving as a core material. 
   
   
       7 . The production method of a self-coated single crystal according to  claim 1 , wherein the core of the single crystal consists of a material which is one of Yb:YAG, Nd:YAG, Yb:LuAG, Nd:LuAG, Ti:Sapphire, Cr:Sapphire, Ce:GSO, Ce:LSO, Ce:LiCAF, Ho:LuLF, HoTm:YLT, Ce:PrF 3 , LN and LT. 
   
   
       8 . The production method of a single crystal according to  claim 1 , wherein a composition of a starting material is a composition obtained by shifting a positive ion ratio in a composition of a target single crystal by 5 to 15%. 
   
   
       9 . A production apparatus of a single crystal which carries out pulling-down growth of the single crystal from a hole formed in a bottom portion of a crucible, wherein means for giving a temperature gradient in the vicinity of a solid-liquid interface is provided. 
   
   
       10 . The production apparatus of a single crystal according to  claim 9 , wherein the means for giving a temperature gradient is constituted of a planar protruding portion having an outer diameter (S) which is not greater than fivefold of an inner diameter (B) of the crucible around the hole of the crucible on an exit side. 
   
   
       11 . The production apparatus of a single crystal according to  claim 10 , wherein 1.2<B/S<5 is achieved. 
   
   
       12 . The production apparatus of a single crystal according to  claim 11 , wherein 1.5<B/S<4.5 is achieved. 
   
   
       13 . The production apparatus of a single crystal according to  claim 10 , wherein means for flowing an inert gas from a lower side toward an upper side of the crucible is provided.